1. Field of the Invention
The present invention relates generally to a broadband wireless communication system, and in particular, to an apparatus and method for reducing Media Access Protocol (MAP) channel overhead.
2. Description of the Related Art
Today, many wireless communication technologies have been proposed as candidates for high-speed mobile communications. Among them, Orthogonal Frequency Division Multiplexing (OFDM) is thought of as most promising for future-generation wireless communications. OFDM was adopted for Wireless Metropolitan Area Network (WMA) of Institute of Electrical and Electronics Engineers (IEEE) 802.16 standards family called the 3.5th generation technology. OFDM is also expected to find its use in most of 4th generation wireless communication technologies, which will be deployed by 2010.
Among the IEEE 802.16 standardization working groups, major wireless communication standards are IEEE 802.16d and 802.16e. These two standards are further branched into single carrier, OFDM, and Orthogonal Frequency Division Multiple Access (OFDMA). The IEEE 802.16d/e OFDM standards define structures of downlink and uplink frames using time-frequency resources and radio channel allocation based on radio channel status within a frame in order to effectively deliver intended digital bit information to a receiver.
A MAP channel structure complying with the OFDM standards is composed of a DownLink-MAP (DL-MAP) channel and an UpLink-MAP (UL-MAP) channel. The DL-MAP channel provides information about users to receive downlink bursts and positions of downlink bursts within a downlink frame. Downlink bursts carry actual data sent from a Base Station (BS). The UL-MAP channel provides information about users that are to send uplink bursts and positions of uplink bursts within an uplink frame. Uplink bursts carry actual data sent from users, i.e. Mobile Stations (MSs). By the UL-MAP channel, the BS indicates users to send their uplink data and positions of the uplink data in the uplink frame. A burst refers to a set of data to which the same Modulation and Coding Scheme (MCS) is applied. A downlink or uplink burst has at least one subchannel and at least one symbol. Symbols are physically arranged in order of time. For example, a kth symbol is followed by a (k+1)th symbol in time. In contrast, an sth subchannel may or may not be physically adjacent to an (S+1)th subchannel. Due to the frequency selective feature of broadband transmission, subchannels are logically rearranged so OFDM subcarriers of each subchannel are not successive physically.
As described above, the conventional IEEE 802.16 OFDMA system selects appropriate subchannels for users according to their radio channel status using a variety of subchannel allocation schemes and configures a frame by allocating data for users based on a subchannel-symbol, to thereby flexibly arrange downlink and uplink bursts in the frames. However, as the freedom of resource allocation increases, control information to be sent increases as much. Control information about positions of data to be notified to users adds to overhead of the DL-MAP and the UL-MAP channels when data for a plurality of users co-exist in one frame. Especially since all MSs have to receive the MAP information, a BS modulates and encodes the MAP channels using an MCS robust enough to allow a remotest MS to receive the MAP information. As a result, significant resources are used to send the MAP channels at the sacrifice of a size of payload carrying actual data.